E coli Accumulation behind an Obstacle

Abstract

This paper describes our findings regarding the accumulation of motile bacte-ria at the rear of a confined obstacle and the physical description of the me-chanisms at play. We found that the modification of flow due to the presence of the obstacle produces vorticity that favor the diffusion of bacteria towards the downstream stagnation point. By testing different flow rates, we deter-mined the range in which bacteria accumulate. More interestingly, we observe that hydrodynamic interaction between the bacteria and the top and bottom surface of the microfluidic chip maintain the bacteria in the region where the flow velocity is lower than their own velocity. In the case of non-motile bacte-ria, this effect is not observed because bacteria follow the streamlines as pas-sive tracers do.